Air Compressor with Adjustable Speed Drive

Summary

Air Compressor with Adjustable Speed Drive

Air Compressor: Adjustable Speed vs. Constant Speed

Adjustable Speed Drive (ASD) control of oil-lubricated or oil-free rotary screw air compressors is more efficient than load/unload, modulating, or modulating with unloading flow control.

Synopsis:

Variable speed compressors have been available since the 1990s in sizes up to 700 hp and have achieved significant market penetration.

Depending upon the air flow profile, ASD compressors can provide significant energy savings when compared with rotary screw compressors with either load/unload or modulating controls. Very small compressors equipped with on-off controls tend to be very efficient. Adjustable speed compressors are ideal for service as trim compressors in multiple compressor installations. In this scenario, conventional fixed speed compressors are operated efficiently at full-rated output to serve base loads while fluctuating air demands are efficiently met by the variable speed compressor.

Energy savings are extremely application dependent and vary with a plant's air flow profile. Compressors that supply less than rated load much of the time offer significant savings. ASD compressors also allow for the air pressure to be reduced as you are not charging a receiver to 110-psig or more when 100-psig is required. In this case, the receiver is not being used to store air so your compressor can be unloaded. Benefits may arise due to pressure stabilization in the plant. Additional savings occur as compressed air storage can be reduced when adjustable speed compressors are placed in the engine room. Power factor is improved when pulse width modulated drives are used.

Energy Savings: 38%

Energy Savings Rating: Approved Measure What's this?

Level	Status	Description
1	Concept not validated	Claims of energy savings may not be credible due to lack of documentation or validation by unbiased experts.
2	Concept validated:	An unbiased expert has validated efficiency concepts through technical review and calculations based on engineering principles.
3	Limited assessment	An unbiased expert has measured technology characteristics and factors of energy use through one or more tests in typical applications with a clear baseline.
4	Extensive assessment	Additional testing in relevant applications and environments has increased knowledge of performance across a broad range of products, applications, and system conditions.
5	Comprehensive analysis	Results of lab and field tests have been used to develop methods for reliable prediction of performance across the range of intended applications.
6	Approved measure	Protocols for technology application are established and approved.

Simple Payback, New Construction (years): 1.5 What's this?

Simple Payback is one tool used to estimate the cost-effectiveness of a proposed investment, such as the investment in an energy efficient technology. Simple payback indicates how many years it will take for the initial investment to "pay itself back." The basic formula for calculating a simple payback is:

Simple Payback = Incremental First Cost / Annual Savings

The Incremental Cost is determined by subtracting the Baseline First Cost from the Measure First Cost.

For New Construction, the Baseline First Cost is the cost to purchase the standard practice technology. The Measure First Cost is the cost of the alternative, more energy efficienct technology. Installation costs are not included, as it is assumed that installation costs are approximately the same for the Baseline and the Emerging Technology.

For Retrofit scenarios, the Baseline First Cost is $0, since the baseline scenario is to leave the existing equipment in place. The Emerging Technology First Cost is the Measure First Cost plus Installation Cost (the cost of the replacement technology, plus the labor cost to install it). Retrofit scenarios generally have a higher First Cost and longer Simple Paybacks than New Construction scenarios.

Simple Paybacks are called "simple" because they do not include details such as the time value of money or inflation, and often do not include operations and maintenance (O&M) costs or end-of-life disposal costs. However, they can still provide a powerful tool for a quick assessment of a proposed measure. These paybacks are rough estimates based upon best available data, and should be treated with caution. For major financial decisions, it is suggested that a full Lifecycle Cost Analysis be performed which includes the unique details of your situation.

The energy savings estimates are based upon an electric rate of $.09/kWh, and are calculated by comparing the range of estimated energy savings to the baseline energy use. For most technologies, this results in "Typical," "Fast" and "Slow" payback estimates, corresponding with the "Typical," "High" and "Low" estimates of energy savings, respectively.

Details

Air Compressor with Adjustable Speed Drive

Air Compressor: Adjustable Speed vs. Constant Speed

Adjustable Speed Drive (ASD) control of oil-lubricated or oil-free rotary screw air compressors is more efficient than load/unload, modulating, or modulating with unloading flow control.

Item ID: 90

Sector: Industrial

Energy System: Process Loads & Appliances--Industrial Processes

Synopsis:

Variable speed compressors have been available since the 1990s in sizes up to 700 hp and have achieved significant market penetration.

Baseline Example:

Baseline Description: Oil Lubricated Rotary Screw Compressor with Modulation Flow Control
Baseline Energy Use: 4758 kWh per year per hp

Comments:

The baseline energy use is for a small industrial plant with 24 hours per day operation. Their peak air demand of about 230 cfm is met with a 60 hp oil lubricated rotary screw compressor with modulation controls. The air profile for the plant calls for lower consumption during the night shift, with a dip around lunch time, and continuous but lower consumption during the week ends. Atlas Copco claims that about 64% of all industrial plants have a similar profile.

Manufacturer's Energy Savings Claims:

Savings Range: From 35% to 40%

Comments:

Manufacturers claim energy savings of 35% to 40% (according to Atlas Copco).

Best Estimate of Energy Savings:

"Typical" Savings: 38%
Energy Savings Reliability: 6 - Approved Measure

Comments:

Installation of an ASD compressor would reduce energy consumption of 285,526 kWh/year by 38% resulting in an annual energy savings of 108,500 kWh/year. This is equivalent to a savings of 1,808 kWh/year per hp. Savings would be less for one or two shift operations, but much greater if a larger ASD compressor (up to 350 hp) was put into trim service at an industrial facility with a larger air load.

Note that this is not 38% of a facility’s total compressed air system energy use, but reflects only the energy use of the trim compressor that is unloading or modulating to meet variable air demands. Compressors that are base loaded would continue to operate in a base loaded manner.

This is a deemed measure under the October 1, 2014 BPA "Energy Efficiency Implementation Manual." The deemed amount is described in a projects payment table.

Energy Use of Emerging Technology:

2,950 kWh per hp per year What's this?

Energy Use of an Emerging Technology is based upon the following algorithm.

Baseline Energy Use - (Baseline Energy Use * Best Estimate of Energy Savings (either Typical savings OR the high range of savings.))

Technical Potential:
Units: hp
Potential number of units replaced by this technology: 194,398
Comments:

Air compressors greater than 20 hp and less than or equal to 500 hp account for about 39,885 GWh of electrical energy consumption in the U.S. (From the USDOE's "United States Industrial Electric Motor Systems Market Opportunities Assessment"). The number of motors by air compressor size range are:

21—50 hp, 138,743 motors;
51--100 hp, 36,450 motors;
101--200 hp, 27,288 motors;
201--500 hp, 16,275 motors.

A conservative estimate of the total compressor drive motor horsepower is made by multiplying the number of motors times the lower value of the motor horsepower range. This yields: 2,913,603 + 1,858,950 + 2,756,088 + 3,271,275 = 10,799,916 drive motor hp in the U.S. that are candidates for VSD retrofits.

The U.S. total compressor motor hp will be pro-rated by population to estimate the total compressor hp in the Northwest region, which has about 4% of the national population. 0.04 x 10,799,916 hp = 431,997 total motor hp.

This number will be reduced by 40% to reflect the number of compressors in trim versus base load service. Without market survey data, it will be assumed that 25% of all trim compressors are currently VSD units. Incorporation of these assumptions yields a total compressor hp of:

0.6 x 0.75 x 431,997 hp x = 194,398 compressor hp.

Regional Technical Potential:
0.35 TWh per year
40 aMW
What's this?

Regional Technical Potential of an Emerging Technology is calculated as follows:

Baseline Energy Use * Estimate of Energy Savings (either Typical savings OR the high range of savings) * Technical Potential (potential number of units replaced by the Emerging Technology)

First Cost:

Installed first cost per: hp
Emerging Technology Unit Cost (Equipment Only): $902.00
Baseline Technology Unit Cost (Equipment Only): $653.00

Comments:

The equipment cost for a 20 hp Atlas Copco VSD rotary screw compressor is $15,895 (2014 quote). Freight and installation costs amount to an additional $2,150 for a total installed cost of $18,045 ($902/hp). The RS Means 2015 Facilities Construction Cost Data publications lists a 25 hp 2-stage reciprocating constant-speed compressor as having an equipment (including a 250 gal tank) plus labor cost of $16,325 ($653/hp).

Cost Effectiveness:

Simple payback, new construction (years): 1.5

Simple payback, retrofit (years): N/A

What's this?

Cost Effectiveness is calculated using baseline energy use, best estimate of typical energy savings, and first cost. It does not account for factors such as impacts on O&M costs (which could be significant if product life is greatly extended) or savings of non-electric fuels such as natural gas. Actual overall cost effectiveness could be significantly different based on these other factors.

Reference and Citations:

David Prator, 10/01/1998. Variable Speed Drives Cut Compressor Energy Costs
Plant Engineering

Chris Beals, 05/09/2006. Unwinding the Spin on Variable Speed Drive Air Compressors
Twenty-Eighth Industrial Energy Technology Conference

Kaeser Compressor, 01/24/2014. Kaeser’s new ESD rotary screw compressors: Space- and Energy Savings
KAESER Press Release

N. Anglani, 09/06/2010. Variable speed drive air compressors: an analytic approach to energy saving evaluation
International Conference on Electrical Machines

Rank & Scores

Air Compressor with Adjustable Speed Drive

There is no TAG available for this technology.